Get documents about "Threads
Shared by: LBY2ks
-
Stats
- views:
- 13
- posted:
- 11/8/2011
- language:
- English
- pages:
- 46
Document Sample
Multithreaded Programming
using Java Threads
Prof. Rajkumar Buyya
Cloud Computing and Distributed Systems (CLOUDS) Laboratory
Dept. of Computer Science and Software Engineering
University of Melbourne, Australia
http://www.cloudbus.org/~raj or http://www.buyya.com
1
Agenda
Introduction
Thread Applications
Defining Threads
Java Threads and States
Priorities
Accessing Shared Resources
Synchronisation
Assignment 1:
Multi-Threaded Math Server
Advanced Issues:
Concurrency Models: master/worker, pipeline, peer processing
Multithreading Vs multiprocessing
2
A single threaded program
class ABC
{
….
public void main(..) begin
{
… body
..
end
}
}
3
A Multithreaded Program
Main Thread
start
start start
Thread A Thread B Thread C
Threads may switch or exchange data/results
4
Single and Multithreaded
Processes
threads are light-weight processes within a process
Single-threaded Process Multiplethreaded Process
Threads of
Execution
Single instruction stream Multiple instruction stream
Common
Address Space
5
Multithreaded Server: For Serving
Multiple Clients Concurrently
Client 1 Process Server Process
Server
Threads
Internet
Client 2 Process
6
Web/Internet Applications:
Serving Many Users Simultaneously
PC client
Internet
Server
Local Area Network
PD
A
7
Modern Applications need Threads (ex1):
Editing and Printing documents in background.
Printing Thread
Editing Thread
8
Multithreaded/Parallel File Copy
reader()
{ writer()
- - - - - - - - - buff[0] {
- - - - - - - - - - -
lock(buff[i]); lock(buff[i]);
read(src,buff[i]); buff[1]
write(src,buff[i]);
unlock(buff[i]); unlock(buff[i]);
- - - - - - - - - - - - - - - - - - -
- }
}
Cooperative Parallel Synchronized
Threads
9
Levels of Parallelism
Code-Granularity
Code Item
Sockets/ Task i-l Task i Task i+1 Large grain
PVM/MPI (task level)
Program
func1 ( ) func2 ( ) func3 ( )
{ { { Medium grain
.... ....
Threads .... ....
....
....
(control level)
} } }
Function (thread)
Fine grain
a ( 0 ) =.. a ( 1 )=.. a ( 2 )=.. (data level)
Compilers b ( 0 ) =.. b ( 1 )=.. b ( 2 )=..
Loop (Compiler)
Very fine grain
CPU + x Load (multiple issue)
With hardware
10
What are Threads?
A piece of code that run in concurrent with
other threads.
Each thread is a statically ordered sequence of
instructions.
Threads are being extensively used express
concurrency on both single and
multiprocessors machines.
Programming a task having multiple threads of
control – Multithreading or Multithreaded
Programming.
11
Java Threads
Java has built in thread support for
Multithreading
Synchronization
Thread Scheduling
Inter-Thread Communication:
currentThread start setPriority
yield run getPriority
sleep stop suspend
resume
Java Garbage Collector is a low-priority thread.
12
Threading Mechanisms...
Create a class that extends the Thread class
Create a class that implements the Runnable
interface
Thread Runnable Thread
MyThread MyClass
(objects are threads) (objects with run() body)
[a] [b]
13
1st method: Extending Thread
class
Create a class by extending Thread class and override
run() method:
class MyThread extends Thread
{
public void run()
{
// thread body of execution
}
}
Create a thread:
MyThread thr1 = new MyThread();
Start Execution of threads:
thr1.start();
Create and Execute:
new MyThread().start();
14
An example
class MyThread extends Thread {
public void run() {
System.out.println(" this thread is running ... ");
}
}
class ThreadEx1 {
public static void main(String [] args ) {
MyThread t = new MyThread();
t.start();
}
}
15
2nd method: Threads by
implementing Runnable interface
Create a class that implements the interface Runnable and
override run() method:
class MyThread implements Runnable
{
.....
public void run()
{
// thread body of execution
}
}
Creating Object:
MyThread myObject = new MyThread();
Creating Thread Object:
Thread thr1 = new Thread( myObject );
Start Execution:
thr1.start();
16
An example
class MyThread implements Runnable {
public void run() {
System.out.println(" this thread is running ... ");
}
}
class ThreadEx2 {
public static void main(String [] args ) {
Thread t = new Thread(new MyThread());
t.start();
}
}
17
Life Cycle of Thread
new
start()
I/O completed
ready
Time expired/ resume()
notify() interrupted
sleeping blocked
waiting
dispatch
sleep()
wait() suspend()
running Block on I/O
completion
stop() dead
18
A Program with Three Java Threads
Write a program that creates 3 threads
19
Three threads example
class A extends Thread
{
public void run()
{
for(int i=1;i<=5;i++)
{
System.out.println("\t From ThreadA: i= "+i);
}
System.out.println("Exit from A");
}
}
class B extends Thread
{
public void run()
{
for(int j=1;j<=5;j++)
{
System.out.println("\t From ThreadB: j= "+j);
}
System.out.println("Exit from B");
}
}
20
class C extends Thread
{
public void run()
{
for(int k=1;k<=5;k++)
{
System.out.println("\t From ThreadC: k= "+k);
}
System.out.println("Exit from C");
}
}
class ThreadTest
{
public static void main(String args[])
{
new A().start();
new B().start();
new C().start();
}
}
21
Run 1
[raj@mundroo] threads [1:76] java ThreadTest
From ThreadA: i= 1
From ThreadA: i= 2
From ThreadA: i= 3
From ThreadA: i= 4
From ThreadA: i= 5
Exit from A
From ThreadC: k= 1
From ThreadC: k= 2
From ThreadC: k= 3
From ThreadC: k= 4
From ThreadC: k= 5
Exit from C
From ThreadB: j= 1
From ThreadB: j= 2
From ThreadB: j= 3
From ThreadB: j= 4
From ThreadB: j= 5
Exit from B
22
Run2
[raj@mundroo] threads [1:77] java ThreadTest
From ThreadA: i= 1
From ThreadA: i= 2
From ThreadA: i= 3
From ThreadA: i= 4
From ThreadA: i= 5
From ThreadC: k= 1
From ThreadC: k= 2
From ThreadC: k= 3
From ThreadC: k= 4
From ThreadC: k= 5
Exit from C
From ThreadB: j= 1
From ThreadB: j= 2
From ThreadB: j= 3
From ThreadB: j= 4
From ThreadB: j= 5
Exit from B
Exit from A
23
Process Parallelism
int add (int a, int b, int & result)
// function stuff
int sub(int a, int b, int & result) Data
// function stuff Processor
IS1 a
add
pthread t1, t2;
b
pthread-create(&t1, add, a,b, & r1); r1
Processor
pthread-create(&t2, sub, c,d, & r2); c
pthread-par (2, t1, t2); IS2
sub d
r2
MISD and MIMD Processing
24
Data Parallelism
sort( int *array, int count) Data
//......
Processor
//...... do
Sort
“
pthread-t, thread1, thread2; “
“ IS
“ dn/2
pthread-create(& thread1, sort, array, N/2);
pthread-create(& thread2, sort, array, N/2); Processor
pthread-par(2, thread1, thread2);
dn2/+1
Sort “
“
dn
SIMD Processing
25
Thread Priority
In Java, each thread is assigned priority, which
affects the order in which it is scheduled for
running. The threads so far had same default
priority (NORM_PRIORITY) and they are served
using FCFS policy.
Java allows users to change priority:
ThreadName.setPriority(intNumber)
MIN_PRIORITY = 1
NORM_PRIORITY=5
MAX_PRIORITY=10
26
Thread Priority Example
class A extends Thread
{
public void run()
{
System.out.println("Thread A started");
for(int i=1;i<=4;i++)
{
System.out.println("\t From ThreadA: i= "+i);
}
System.out.println("Exit from A");
}
}
class B extends Thread
{
public void run()
{
System.out.println("Thread B started");
for(int j=1;j<=4;j++)
{
System.out.println("\t From ThreadB: j= "+j);
}
System.out.println("Exit from B");
}
}
27
Thread Priority Example
class C extends Thread
{
public void run()
{
System.out.println("Thread C started");
for(int k=1;k<=4;k++)
{
System.out.println("\t From ThreadC: k= "+k);
}
System.out.println("Exit from C");
}
}
class ThreadPriority
{
public static void main(String args[])
{
A threadA=new A();
B threadB=new B();
C threadC=new C();
threadC.setPriority(Thread.MAX_PRIORITY);
threadB.setPriority(threadA.getPriority()+1);
threadA.setPriority(Thread.MIN_PRIORITY);
System.out.println("Started Thread A");
threadA.start();
System.out.println("Started Thread B");
threadB.start();
System.out.println("Started Thread C");
threadC.start();
System.out.println("End of main thread");
}
}
28
Accessing Shared Resources
Applications Access to Shared Resources need
to be coordinated.
Printer (two person jobs cannot be printed at the
same time)
Simultaneous operations on your bank account.
Can the following operations be done at the same
time on the same account?
Deposit()
Withdraw()
Enquire()
29
Online Bank: Serving Many Customers
and Operations
PC client
Internet Bank
Server
Local Area Network
Bank
Database PD
A
30
Shared Resources
If one thread tries to read the data and other
thread tries to update the same data, it leads to
inconsistent state.
This can be prevented by synchronising access
to the data.
Use “Synchronized” method:
public synchronized void update()
{
…
}
31
the driver: 3rd Threads sharing
the same object
class InternetBankingSystem {
public static void main(String [] args ) {
Account accountObject = new Account ();
Thread t1 = new Thread(new MyThread(accountObject));
Thread t2 = new Thread(new YourThread(accountObject));
Thread t3 = new Thread(new HerThread(accountObject));
t1.start();
t2.start();
t3.start();
// DO some other operation
} // end main()
}
32
Shared account object
between 3 threads
class MyThread implements Runnable {
Account account;
public MyThread (Account s) { account = s;}
public void run() { account.deposit(); }
} // end class MyThread
class YourThread implements Runnable { account
Account account;
public YourThread (Account s) { account = s;}
(shared
public void run() { account.withdraw(); } object)
} // end class YourThread
class HerThread implements Runnable {
Account account;
public HerThread (Account s) { account = s; }
public void run() {account.enquire(); }
} // end class HerThread
33
Monitor (shared object access):
serializes operation on shared object
class Account { // the 'monitor'
int balance;
// if 'synchronized' is removed, the outcome is unpredictable
public synchronized void deposit( ) {
// METHOD BODY : balance += deposit_amount;
}
public synchronized void withdraw( ) {
// METHOD BODY: balance -= deposit_amount;
}
public synchronized void enquire( ) {
// METHOD BODY: display balance.
}
}
34
Multithreaded Server Multithreaded Server
Server Process
Client Process
Server
Threads
Client Process
User Mode
Kernel Mode
Message Passing
Facility
35
Assignment 1: Multithreaded MathServer –
Demonstrates the use of Sockets and Threads
A Client Program “sqrt 4.0”
What is sqrt(10)? Multithreaded
MathServer
“2.0”
(sin, cos, sqrt, etc.)
A Client Program
What is sin(10)?
A Client
Program in “C” A Client
What is sin(10)? Program in “C++”
What is sin(10)?
36
A Multithreaded Program
MathThreads
start start start
MathSin MathCos MathTan
join join join
MathThreads
37
Thread Programming models
Thread concurrency/operation models
The master/worker model
The peer model
A thread pipeline
38
The master/worker model
Program Resources
Workers
taskX
Files
Master Databases
taskY
main ( )
Input (Stream)
Disks
taskZ
Special
Devices
39
The peer model
Program Resources
Workers
Input taskX
Files
Databases
taskY
Disks
taskZ
Special
Devices
40
A thread
A thread pipeline pipeline
Program Filter Threads
Stage 1 Stage 2 Stage 3
Input (Stream)
Resources Files Files Files
Databases Databases Databases
Disks Disks Disks
Special Devices Special Devices Special Devices
41
Multithreading and
Multiprocessing Deployment
issues
On Shared and distributed
memory systems
42
Multithreading - Multiprocessors
Process Parallelism
CPU
P1
P2 CPU
P3 CPU
time
No of execution processes <= the number of CPUs
43
Multithreading on Uni-processor
Concurrency Vs Parallelism
Process Concurrency
P1
P2 CPU
P3
time
Number of Simultaneous execution units > number of CPUs
44
Multi-Processing (clusters & grids)
and Multi-Threaded Computing
Threaded Libraries, Multi-threaded I/O
Application
Application Application
Application
CPU
CPU
CPU CPU CPU CPU
Better Response Times in Higher Throughput for
Multiple Application Parallelizeable Applications
Environments
45
References
Rajkumar Buyya, Thamarai Selvi,
Xingchen Chu, Mastering OOP with
Java, McGraw Hill (I) Press, New Delhi,
India, 2009.
Sun Java Tutorial – Concurrency:
http://java.sun.com/docs/books/tutorial/esse
ntial/concurrency/
46
